Method and apparatus for telephone line testing

ABSTRACT

A method and apparatus for qualifying a telephone transmission line for XDSL communication services is disclosed. The system includes a modem, located at the customer premises to be connected. The modem analyzes actual signals to determine the electrical characteristics of the communication channel associated with the customer premises. The modem includes a transmitter, receiver and controller to generate test signals and receive responses. The modem then analyzes the data to generate an output value indicative of the electrical characteristics of the communication channel being tested. This output value is then displayed to a user or transmitted over the communication channel to a network. The system thereby eliminates the necessity of dispatching a technician to test the telephone line, and provides more accurate test results than those achievable at the network-side of the connection alone.

RELATED APPLICATIONS

[0001] This is a Continuation-In-Part Application of U.S. applicationSer. No. 09/239,591 filed on Jan. 29, 1999.

TECHNICAL FIELD

[0002] This invention relates generally to telephone line testing andmore particularly to a method and apparatus for qualifying a customernode of a public switched telephone network for digital communicationsservices.

BACKGROUND OF THE INVENTION

[0003] The characteristics of telephone lines vary greatly. Typicaltelephone lines connecting a customer premises to a public switchtelephone network (PSTN) vary in terms of length, wire gauge, amount ofbridged tap, background noise, loading coils, and other aspects. Inaddition, faults may be present along the telephone lines such as: ashort circuit, an open circuit, conductor leakage, a short circuit to apower line, or induction interference from a power line. The operationand communications integrity of loop transmission systems depends on thetelephone line characteristics. Loop transmission systems include aplain old telephone system (POTS), and digital subscriber line servicessuch as an integrated services digital network (ISDN), high speeddigital subscriber line (HDSL), very high speed digital subscriber line(VDSL), or asymmetric digital subscriber line (ADSL). These digitalsubscriber line services are commonly referred to as XDSL services.

[0004] Because the integrity of XDSL communications services depend onthe quality of the transmission line connection, it is desirable to testthe telephone line connecting a customer premises to the PSTN todetermine whether the telephone line will support the desiredtransmission service. It is also desirable to test the line to diagnosethe source of transmission faults or interference.

[0005] Presently, two methods are commonly employed to test telephonetransmission lines: (1) central office or remote terminal automated linetest systems, and (2) a dispatched technician with a hand-held test set.In the first case, a line test command is sent from a centralized loopmaintenance system to a network terminating node (NTN) such as a localtelephone switch or carrier system located in a central office or remoteequipment site. In response, the NTN connects the line to be testedthrough a series of relays to a system that performs electricalmeasurements of the telephone transmission line. The results of thesemeasurements are then reported back to the loop maintenance system.

[0006] In the second case, a technician is dispatched to connect ahand-held test set to the telephone transmission line to be tested atone of the following locations: (1) the central office main distributingframe, (2) the network interface device (NID) at the customer node, or(3) an intermediate point such as a serving area interface point. Usingthe hand-held test set, the technician measures the electricalcharacteristics of the line and reports the results of the test to theloop maintenance center. In either case, the electrical characteristicsof the line are known, and a determination can then be made as to thetype of digital communications services the telephone transmission linewill support.

[0007] There are several shortcomings, however, with the present methodsfor qualifying telephone transmission lines for digital communicationservices. In the first case, transmission loops served from some networkterminating nodes, such as digital subscriber line access multiplexersand digital loop carrier systems, may not provide metallic test accessto the telephone transmission line or the line measurement unit. In thecase where telephone service is not yet activated, the telephonetransmission line may not be connected to an NTN at all. In thesesituations, it would not be possible to perform an automated line testfrom the network-end of the line. Furthermore, transmission loops whichare connected to an NTN with a metallic test bus and a line measurementunit, may only respond to test frequencies within the sub-4 kHz band dueto bandwidth limitations of the test bus or the line measurement unit.In addition, background interference noise at the customer node may bedifficult to observe with testing equipment located only at the NTN.

[0008] Dispatching a technician to test the telephone transmission linehas the obvious shortcoming of increasing the time and expense toprovide digital communication services to customers. This results fromthe need for personnel to perform these tests, and the need to providetechnicians with testing equipment.

[0009] The present invention overcomes the shortcomings of presenttelephone transmission line testing methods by providing a modem at thecustomer premises for testing and qualifying the customer connection tothe PSTN for XDSL communication services.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the invention, referenceshould now be had to the embodiments illustrated in greater detail inthe accompanying drawings and described below by way of examples of theinvention.

[0011] In the drawings:

[0012]FIG. 1 is a schematic block diagram of one embodiment of thepresent invention used in connection with a computer located at acustomer premises.

[0013]FIG. 2 is a schematic block diagram of one embodiment of the modemfor use in the telephone line testing scenario of FIG. 1.

[0014]FIG. 3 is a perspective view of one embodiment of a direct accessarrangement testing device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0015] Referring to FIG. 1, there is shown a schematic block diagram ofan embodiment of the present method of testing a telephone transmissionline. The system shown in FIG. 1 comprises a modem 10 located at thecustomer premises 12 which is connected by way of transmission line 14to the network interface device 16 at the customer premises 12.Transmission line 14 will typically comprise the modem line connected toa common telephone wall jack, and associated wiring from the wall jackto the network interface device 16. Alternatively, transmission line 14can comprise the modem line connected directly into the networkinterface jack in the NID 16. It is contemplated that the modem 10 willtypically be part of a digital communications device such as a computer18 or will be connected to such a device as shown in FIG. 1 bytransmission line 20. XDSL modems are commonly included in today'spersonal computer systems. Unlike customer-end XDSL modems to date,however, modem 10 includes wideband loop testing and reportingfunctions. Between the network interface device 16 at the customerpremises 12 and the public switch telephone network (PSTN) 22, is thetelephone transmission line 24 to be tested. Of course, the PSTN couldalso represent a digital network.

[0016] Computer 18 is shown as part of a representative digitalcommunications system at a customer premises 12. The modem 10 istypically a necessary part of computer 18 which allows computer 18 totransmit and receive digital signals over telephone transmission line24. For purposes of line testing, however, computer 18 is not necessaryif modem 10 is equipped with a user interface for displaying the resultsof the telephone transmission line test. It is to be understood thatcomputer 18 is shown for illustration purposes and could beinterchanged, for example, with other equipment that generates acommunications signal to be sent over the telephone transmission line24.

[0017] Referring to FIG. 2, an embodiment of the modem 10 comprises atransmitter/receiver 26 and direct access arrangement (DAA) 28. Thetransmitter/receiver 26 includes a modem controller 30 such as amicroprocessor, associated memory 32, application specific integratedcircuit (ASIC) 34, and a digital signal processor (DSP) 36. Thesecomponents communicate along signal paths 38, 40 and 42.

[0018] The direct access arrangement 28 includes a digital-to-analog(D/A) and analog-to-digital (A/D) converter 44 and telephone interfacecircuitry 46. The converter 44 communicates with the DSP 36 andinterface 46 along signal paths 48 and 50, respectively. The interface46 transmits signals to and receives signals from the network interfacedevice 16 along transmission line 14.

[0019] The modem controller 30, memory 32, ASIC 34, and DSP 36 define atransmitter for generating test signals on telephone transmission line24. Modem controller 30, memory 32, ASIC 34 and DSP 36 also define areceiver for detecting signals in response to test signals transmittedto telephone transmission line 24.

[0020] The connection and operation of the components thus far describedin modem 10 are well known.

[0021] In addition, modem 10 preferably includes a user interface 48 incommunication with modem controller 30 along signal line 50 fordisplaying the telephone transmission line test results to a user.

[0022] In operation, customers who desire DSL 20 services would connectthe modem 10 to a wall jack at the customer premises or the networkinterface jack in the network interface device 16. The modem 10 performsa series of telephone line tests to qualify the line for its desired useand/or to diagnose the source of transmission interference. The testresults are presented to the user by the user interface 48 or,alternatively, can be transmitted to, for example, computer 18 fordisplay, or along transmission line 24 to a communications serviceprovider. In this manner, the telephone transmission line 24 can bepre-qualified for the desired communications service.

[0023] To display an output indicative of the electrical characteristicsof telephone transmission line 24, the modem 10 performs a series oftests. The testing sequence and logic is stored in memory 32 andexecuted by memory controller 30 in cooperation withtransmitter/receiver 26 and DAA 28. The following functions are carriedout by the modem 10 in qualifying the telephone transmission line 24.One function is line monitoring which consists of measuring backgroundnoise power in one or more frequency bands in a frequency range ofapproximately 0 Hz to 5 MHz. Another function is measurement of AC or DCvoltage between the tip and ring, tip and ground, and ring and groundterminals of the telephone transmission line 24. Stimulus and responsetesting is also performed by the modem 10 in the form of transmittingtest tones, receiving response signals in response to the test tones,and analyzing the amplitude and phase of the signal reflections from thetransmission line 24. Additionally, modem 10 transmits test pulses,receives response signals in response to the test pulses, and analyzesthe amplitude and delay of the pulse reflections from the transmissionline 24. Additional functionality includes measurement of resistancebetween the tip and ring, tip and ground, and ring and ground terminalsof transmission line 24, as well as measurement of the capacitancebetween the tip and ring terminals of transmission line 24.

[0024] Depending upon the communication service desired by the customer,a series of measurements could be performed with some of the testsperformed more than once, or not at all, depending on the systemconfiguration or the results of earlier tests. In addition, oralternatively, during a test sequence, the end-user could be instructedby the modem controller 30 via the user interface 48 to perform certainactions such as to place telephones on or off hook.

[0025] At the conclusion of the sequencing and 15 analysis, atransmission line quality value is developed as a function of the testresults.

[0026] One scenario for deriving the line quality value is as follows.The user is asked to indicate the type of DSL transmission system forwhich the line analysis is being performed. For example: HDSL, ADSL, orISDN. From this, assumptions are made for the typical transmittedfrequency band(s), signal power, modulation method, and coding, amongother things.

[0027] The broadband attenuation of the line is estimated by applying avoltage step to the line 24 and measuring the time-constant of theresulting current flow. The time-constant estimates the linecapacitance, from which the line length is inferred. The estimation ofthe broadband attenuation could further be refined by applying a shortvoltage pulse to the line and measuring the number and amplitude of theobserved echoed pulses. From these pulses, the presence of bridged tapscan be ascertained. An additional attenuation allowance would then bemade for each bridged tap. By applying a single or multiple tonefrequency sweep to the line and observing the reflected signals,nonlinear distortion and the presence of a loading coil can also bedetected. In addition, the background line noise would be preferablymeasured in one or more frequency bands. If the line response indicatesthe presence of a loading coil, then the line is not suitable forbroadband DSL service. This would be indicated to the user orservice-provider.

[0028] With knowledge of the nominal transmitted signal power and theestimated line attenuation from the measurements mentioned above, thereceived signal power is predicted. The noise power is predicted fromthe measured background noise, and the measured nonlinear distortion. Apredicted signal-to-noise ratio (SNR) value is then estimated. For aknown transmission method (modulation type, transmit power, coding type,bandwidth) the achievable bit-rate is derived from the SNR. Forasymmetric transmission systems (such as ADSL), a SNR estimate isderived separately for the upstream and downstream directions. Thus, aseparate bit-rate capacity estimate is provided for each direction oftransmission.

[0029] This bit-rate capacity is then represented as a line qualityvalue which is then displayed to the end user by way of the userinterface 48. The customer could then relay the line test results to thecommunications service provider. Alternatively, the test results couldbe transmitted to the service provider over transmission line 24.

[0030] With the preferred implementation of the line testing method,line testing would be performed in a single-ended manner. In otherwords, the test is conducted at the customer premises only, and notesting equipment is required at the other end of telephone transmissionline 24. Of course, as an alternative implementation, a double-endedtest could be performed involving coordinating testing functions at boththe customer end of telephone transmission line 24 and the network endof telephone transmission line 24. In the double-ended testing scenario,test signals can be transmitted and received by the modem 10 and thePSTN 22.

[0031] The testing procedures described above can be initiated by eitherthe end user at the customer premises or by way of an initiation messagefrom the service provider or the local network provider via the DSL pathor dial-up voice band modem connection.

[0032] Referring now to FIG. 3, there is shown a perspective view of oneembodiment of a direct access arrangement device 28 according to thepresent invention. The device is a hand-held test set, connected by wayof a transmission line 14 to a network interface device (NID) 16 at thecustomer premises. In the example shown in FIG. 3, the transmission lineis a standard telephone line with RJ-11 connectors 60, 62 for connectingto the NID 16 and PSTN by way of the telephone transmission line 24. Ifthe device is being used at the network central office, a different typeof communication cable may be used to interface with the maindistribution frame (MDF) or switch location associated with a particularcustomer's loop.

[0033] The test set is small in size and can be hand-held. For example,the set may be 7×4×2 inches or less. For easy portability, a belt-clip70 can be affixed to one side of the device. Preferably, the device isbattery powered, and activated with a power switch 74 after connection.The user interface 100 includes two indicators such as LEDs 102, 104which preferably can each indicate red or green and can flash on and offor be lit continuously.

[0034] In operation, the test set qualifies a customer lop for XDSLcommunications, the loop being from between the ADSL terminationunit-remote (ATU-R) to the ATU-Central Office (ATU-C). Once connected,the test set performs at least several of the line tests discussedabove, including attempting to synchronize as an ADSL modem. The testset is capable of inter-operating with the Alcatel 1000 and/or Cisco6100 digital subscriber loop access multiplexers (DSLAMs), for example.

[0035] Upon power-up, LED 104 indicates that initialization is completeand power is sufficient (solid green light), power is low (flashinggreen light), or that the set has failed its power-up initializationtests (solid or flashing red light). If power-up is successful, the testset continues into the testing phase. At least several of the testsoutlined above are performed including testing for an open circuit oneither the tip or ring terminal. That is, tip to ground, ring to groundand tip to ring voltages are determined. During the testing phase, whilethe unit is performing the tests, LED 102 is blinking green to indicatethat the unit is active. If all of the tests are successful and the unithas determined that the customer loop qualifies for XDSL communications,LED 102 is activated to be solid green. If the tests have failed, theindicator is activated as a solid or flashing red light. However, if theopen circuit test has failed, i.e., there is insufficient voltagedetected between the tip and ring circuits, the indicator alternatesflashing green and red. The alternating green/red signal thus indicatesa possible open loop on the customer circuit. If the open loop issue isresolved, the customer loop may still qualify for XDSL communicationsservices. In this way, the test unit acts as a go/no-go gauge forqualifying a customer loop either at the customer premises, or at thecentral office. When performed at the customer premises, the unit maycommunicate either the test passed, test failed, or test failed withpossible open loop results to the central office.

[0036] The hand-held test set of FIG. 3 thus provides a simple,effective device for qualifying a customer loop for XDSL communicationservices. Of course, the user interface could take many forms, andothers are contemplated by the present invention. Preferably, however,the interface should communicate at least whether the test has passed orfailed and whether a possible open circuit condition exists. Oneindication could accomplish this by a solid, slow blinking and fastblinking signal, respectively, for example. The test set of FIG. 3qualifies the customer loop by indicating whether the customer modemwill be able to synchronize with the network. It does not test foroptimum communications rates.

[0037] While the invention has been described in connection with one ormore embodiments, it is to be understood that the invention is notlimited to these embodiments. On the contrary, the invention covers allalternatives, modifications and equivalents as may be included withinthe scope and spirit of the appended claims.

What is claimed is:
 1. A modem, associated with a customer premises, foranalyzing electrical signals to determine the characteristics of abroadband communication channel between a service provider and acustomer premises, said modem comprising: a transmitter connected tosaid broadband communication channel for delivering signals to saidbroadband communication channel; a receiver connected to said broadbandcommunication channel for receiving response signals from said broadbandcommunication channel; and a modem controller having associated memory,said modem controller in operative communication with said transmitterand said receiver, said modem controller programmed to: command saidtransmitter to generate test signals to stimulate said broadbandcommunication channel; measure response signals received by saidreceiver in response to said test signals; generate an output value as afunction of said test signals and said response signals indicative ofthe electrical characteristics of said broadband communication channeland; transmit said output value over said broadband communicationchannel to said communications service provider to eliminate the needfor a technician dispatch to said customer premises.
 2. The modem ofclaim 1 wherein said broadband communication channel is a telephone lineadapted for XDSL service and said modem controller is programmed to:command said transmitter to generate test signals having a frequencyrange from approximately 0 Hz to 5 MHz to stimulate said telephone line;measure the amplitude, phase and delay of response signals received bysaid receiver in response to said test signals; and generate an outputvalue as a function of said test signals and said response signalsindicative of the electrical characteristics of said telephone line. 3.The modem of claim 2 wherein said modem further comprises a display incommunication with said modem controller for displaying said outputvalue.
 4. The modem of claim 2 wherein said modem controller is furtherprogrammed to transmit said output value to a user interface fordisplaying said output value to a user.
 5. The modem of claim 2 whereinsaid modem controller is further programmed to measure at least two linevoltages associated with said telephone line.
 6. The modem of claim 2wherein said modem controller is further programmed to measurebackground noise in at least one frequency band between approximately 0Hz and 5 MHz.
 7. The modem of claim 2 wherein said modem controller isfurther programmed to measure at least two resistance values associatedwith said telephone line.
 8. The modem of claim 2 wherein said modemcontroller is further programmed to measure a capacitance valueassociated with said telephone line.
 9. At a customer node of a publicswitched telephone network comprising a telephone line associated with acustomer premises, a method of qualifying said customer node forbroadband digital communication services from a service provider withoutthe need for a technician dispatch to said customer node, said customernode having a modem connected to said telephone line at said customerpremises, the method comprising the steps of: transmitting with saidmodem a first plurality of test signals on said telephone line within afrequency range of approximately 0 Hz to 5 MHz; measuring a secondplurality of response signals with said modem received in response tosaid first plurality of test signals; generating an output value as afunction of said first plurality of test signals and said secondplurality of response signals indicative of the electricalcharacteristics of said customer node; and transmitting said outputvalue over said telephone line to said service provider.
 10. The methodof claim 9 further comprising the step of transmitting said output valueto a user interface for displaying said output value to a user.
 11. Themethod of claim 9 further comprising the steps of: measuring a thirdplurality of response signals with said modem received in response totest signals transmitted across said public switched telephone network;and generating an output value as a function of said first plurality oftest signals, said second plurality of response signals, and said thirdplurality of test signals indicative of the electrical characteristicsof said customer node.
 12. The method of claim 11 further comprising thestep of transmitting said output value to a user interface fordisplaying said output vale to a user.
 13. At a customer node of apublic switched telephone network comprising an XDSL modem at saidcustomer node connected to a telephone line, a method of qualifying saidcustomer node for broadband digital communication services from aservice provider without the need for a technician dispatch to saidcustomer node, the method comprising the steps of: generating testsignals on said telephone line within a frequency range of approximately0 Hz to 5 MHz; generating a first plurality of values as a function ofthe amplitude, phase and delay of response signals received in responseto said test signals; generating a second plurality of values indicativeof line voltages associated with said telephone line; generating a thirdplurality of values indicative of resistance associated with saidtelephone line; generating a fourth plurality of values indicative ofcapacitance values associated with said telephone line; generating afifth value indicative of the background noise in at least one frequencyband between approximately 0 Hz and 5 MHz; generating an output value asa function of said first, second, third, fourth and fifth valuesindicative of the electrical characteristics of said customer node; andtransmitting said output value over said telephone line to said serviceprovider.
 14. An apparatus for analyzing electrical signals to qualify abroadband communication channel between a service provider and acustomer premises for XDSL service, said apparatus comprising: a modemprogrammed to generate test signals to stimulate said broadbandcommunication channel, measure response signals in response to said testsignals, measure a line voltage associated with said broadbandcommunication channel, and generate an output value as a function ofsaid test signals, response signals, and line voltage, said output valueindicating either a line pass or line fail; and, a user interfacecomprising at least one indicator activated to indicate said outputvalue.
 15. An apparatus according to claim 14 wherein said broadbandcommunications channel comprises a telephone line having tip and ringconnections, and said line voltage is between said tip and ringconnections.
 16. An apparatus according to claim 14 wherein said userinterface comprises an LED activated green to indicate a line passoutput value and activated red to indicate a line fail output value. 17.An apparatus according to claim 14 wherein said output value includesindicating an open circuit.
 18. A hand-held testing apparatus forqualifying a customer telephone line for XDSL services comprising: amodem for connecting to said telephone line, said modem programmed totransmit a plurality of test signals on said telephone line within afrequency range of approximately 0 Hz to 5 MHz, measure a plurality ofresponse signals in response to said plurality of test signals, measurea line voltage between a tip and ring connection associated with saidtelephone line and generate an output value as a function of saidresponse signals and said line voltage; and a user interface comprisingat least one indicator for communicating said output value to a user,wherein said output value indicates either a line pass or line failresult.
 19. An apparatus according to claim 18 wherein said userinterface comprises an LED activated green to indicate a line passoutput value and activated red to indicate a line fail output value. 20.An apparatus according to claim 18 wherein said output value includes anopen circuit result indicating an insufficient line voltage.
 21. Anapparatus according to claim 20 wherein said user interface is adaptedto indicate an open circuit result.
 22. An apparatus according to claim18 wherein said user interface comprises at least two LEDs, one of saidLEDs indicating a power status of the apparatus, the other of said LEDsindicating said output value.
 23. An apparatus according to claim 18wherein said apparatus is housed in a container smaller thanapproximately 7 inches in length by 4 inches in width by 2 inches indepth.
 24. An apparatus according to claim 23 wherein said containerincludes a belt clip on an exterior side.
 25. An apparatus according toclaim 23 wherein said apparatus is battery operated.